Method of producing steel



1 2,816,017 METHOD OF PRODUCING STEEL Wilhelm Wolf, Dortmund-Eving, and Wilhelm vor dem Esche, Dortmund, Germany, assignors to Hoesch- Westfalenhutte Akfiengesellschaf Dortmund, Germany No Drawing. Application May 12, 1955, Serial No. 507,974

3 Claims. (Cl. 75-46) The present invention relates to a new and improved method of producing steel and more particularly to methods of producing steel having a low chromium con tent starting from iron ores having a high chromium content.

It is well known that the lateritic iron ores comprise a considerable portion of the worlds iron ore deposits. Nevertheless, and despite the purity of these lateritic iron ores withreference to the phosphorous and sulphur contents thereof, and even despite their frequently advantageous location from the point of view of shipping and freighting, these ores have until the present day played only a very minor part in the production of iron and'steel.

The major reason, therefore, is the relatively high chromium content in the lateritic iron ores. As is well known, a major portion of this chromium goes into the pig iron during the smelting of the iron ore. Even relatively low chromium contents in pig iron, for example in excess of 0.20% causes considerable difiiculties during the manufacture of the steel, particularly with respect to the production of soft steel, since chromium is oxidized only at the very end of the blowing process and the oxidation products of the chromium, e. g. the chromites, or chromium spinels, are extremely difiicult to separate from the steel bath due to their very high melting point. Consequently, the production of steel in conventional ways from chromium-containing pig iron generally results in the production of steel containing chromium oxides which steel is therefore of inferior quality.

A method of producing converter iron or steel from chromium-containing pig iron has been developed in which additional metal oxides such as manganese oxide or iron oxides (e. g. in the form of mill or roller scale) are added to the melt before, during or immediately after the hearth or converter blowing so as to reduce the chromium content to less than 0.06%. However, the iron oxides required for the slagging of the chromium is obtained by excessive blowing of the bath and this method has not become common practice in the steel making art because the chromium can be removed only by over-oxidation of the steel. This results in metallurgical and economic disadvantages because the yield of the iron is reduced due to the extremely high iron content in the slag, and the steel is excessively enriched with oxygen.

It is therefore a primary object of the present invention to provide a method of producing steel from iron ores having a high chromium coutent'whereby all of the above disadvantages of the known methods are avoided.

It is another object of the present invention to provide an economical and easily controllable method of producing steel having a low chromium content from iron ores having a high chromium content.

It is still another. object of the present invention to provide a method of producing steel having a low chromium content from iron ore having a high chromium content by adjusting the composition of the iron ore and subjecting the same to preliminary refining prior to the steel-making process. Y

Other objects and advantages of the present inventionwill be apparent from a further reading of the specification and of the appended claims. 7

With these and other objects in view the process of producing steel having a low chromium'content from iron ore having a high chromium content mainly comprises the steps of forming a pig iron containing more than 0.2% chromium and less than 0.8% manganese from an iron ore having a high chromium content, e. g. a lateritic iron ore, subjecting the thus formed pig iron containing more than 0.2% chromium and less than 0.8% manganese to a pro-refining process, e. g. by bl0w-' ing, whereby the chromium content is reduced to less than about 0.1%, and finally subjecting the thus formed tie-chromed iron to a usual converting process to form steel.

Since the iron ores which have a high chromiumcon tent, e. g. lateritic iron ores, generally have a high alumina content of the proportions of the iron ores being so adjusted that the resulting pig iron contains more than 0.2% chromium and less than 0.8% manganese. It is' impossible to smelt these ores per se. For the formation of fluxing slag it is necessary to mix them with one or more other ores. The particular proportions of the ores which must be utilized for this purpose depends upon the particular composition of the ores and the smelting conditions so that exact figures therefor cannot be given. However, the exact proportions for any particular ores can easily be determined by one skilled in the art by simple calculation and/or pre-testing. To obtain a good desulphurisation in the blast furnace it is advantageous to have a certain content of manganese in the pig iron.

The manganese is, similarly to silicon, oxidized in an early stage and eliminated in the subsequent pre-refining step. The temperature hereby is increased and this disturbs the dechroming. Therefore the inventors have recognized that the content of manganese in the pig iron should be less than 0.8%, preferably 0.50.8%.

The ores utilized and the pig iron produced besides the contents of chromium andmanganese also contain the usual amount of phosphorous and the usual or a somewhat increased amount of silicon. It should be noted that all amounts and percentages given in the specification and claims, unless otherwise indicated, refer to amounts and percents by weight.

The primary refining by blowing of pig iron produced according to the present invention to contain more than i 0.2% of chromium and less than 0.8% of manganese results in a reduction in the chromium content of the.

pig iron to less than 0.1%. The thus de-chromed pig iron may then be treated in the usual converting or re-. fining process to obtain without difiiculty a high quality steel having a low chromium content.

The primary purification of the pig iron produced in accordance with the presentinvention, e. g. the blowing of the pig iron, takes place with the addition of heat con-'- suming oxides in either gaseous, liquid, or solid form to the blowing means or to the bath, in order to control the process so that it may be carried out at the lower temperature limit. The inventors have recognized that the temperature at the pre-refining step always should be at the same level. That means, that the temperature at the end of the process should be as-low as at the beginning, e. g."

Patented Dec. 10, 1957 such an extent that under suitable temperature control the chromium content is reduced to below 0.10%. Besides silicon and manganese, also possibly vanadium is converted into slag. The,carbon-contempt the pigqiron should not be considerably;attacked;.;..

After the primary purificatiom-the-slag, is drawn-ofi and thepigiron converted in customary ways, forinstance, blown,- since it now has the composition of regular pre-refinedpig iron.

Bythemethodof'the present-invention, special advantages are obtainednotonly in the blast furnace operation, but; also in the steel smelter In the blast furnace operation considerable leeway einthe slag-and temperature control is obtainedi The silicon content, for instance, which otherwise :is "of decisive importance for the quality otBasic-Besserherpig.iron,- isno longer limited. It is loweredto extremelylow values by the primary purification. I I

Chromium releases upon oxidation more heat than correspondinggquan-tities ofimanganese. It is therefore possible thatchromiunr which otherwise is undesirable in pig;iron may be vutilizedto replace during primarypurificationpart of the oxidation'heatof manganese. It has beenfoundthat the chromiurnoxide-containing slag which is formedaccording to the present. invention during the oxidation-of chromium is obtained at the temperatures in question in a crumbly state and not as a thin liquid. This gives the advantage that the chromium-containingslag of the primary purification can easily be drawn ofif the metal bath.

Pigvironproduced and pre-treated in accordance with the present invention forms in the Thomas plant a-particularly easily converting iron which easily leads'to lownitrogen content-in the finished steel.

I The chromium removal from pig iron in accordance with the method of the present invention can be executed in a channel, inthe pan, in a mixer, Ofin'the steel making vessel, e. g.,.in the converter. It is advantageou'sto prepare'this converter with an acid lining and to conduct the primary purification without the addition'of limestone;

The following example is given to further illustratethe method ofthe present invention, the scope of. the invention'not however beinglimited-z to thespecific' details of the example.

Tapping temperature: l360-142 0 C. I II I The pig iron was pre-refined by blowing with 99% oxygen in the ladle. I

O -consumption for the pro-refining: 9.8 Nm. /t. pig iron Mill-scale for cooling: 45.0 itg f/t-pig iron Amount of the pre-r'efining "slag: 75l0'k'gf/t'. pig iron Temperature at the beginning of the process: I I

I I 1300:1350 c. Temperature at the end "of the process: The pie-refined pig iron-is then blown to steel in a Basic- Be'ssemer converter and the produced steel in this manner has a=nitrogencontcnt of'0.004%. 4 I I The slag of the pre-blowing step is suitable for the production ofspecial steels such as for instance chromiumvariadiu'm-steel, or chromium-manganese-vanadium steel in, for instance, anelectric furnace, since these metals may be easily reduced baclcinto the metal bath.

Without further. analysis, the foregoing-will so fully reveal the gistof the present-invention that others can by applying currentknowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art,.fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should andare intended to be comprehended within the irneaning'aud range of equivalenc e of thefollowing claims;

What claimed as-new and desired to be-secured by Letters Patent is:

1. A method of producingsteel having a low chromium The following cres'aremixed and smelted: content from ironore having a high chromium content,

. B ur- Fe, Mm Cr, srog AltOs,; Ga0;. Mgb, Ore d en,.- percent percen percent percent percent percent percent percent percent 17 an 000 0.91 13.0 3.3 5.3 o ;9 as 45.3 0.01 0 93 0.07 2.2 7.9 0.4 33 57.0 0.12 2.50 3.2 0.7 6.5 1.6 7 48.0 9.0 0.02 9.5 0.8 0.7 4.3

Additions: comprising the steps of sm'elting amixture of afirs't iron 100 kgjdolonn'te/ttpig' iron ore containing oraines 0.2% chromium and a second 220 kg. limestone/t.'pigiron iron ore containingfs'nflicient'manganese so as to form a Coke consumptionz'980 kg./t.pi g'ir'on' pig iron,- at least one of said iron ores also containing Amount of sla'g 540kg.--/t. pig iron phosphorous, silicon and vanadium and the proportions Analysis of sl of said first and saidsecond iron ores 'being so adjusted 28 $0 that the thus formed pig iron contains more than 0.2% 20 A1 0 chromium and less than 0.8% manganese and also con- 41- 0%'C 0 tains phosph'o'rou's", silicon and vanadium; blowing said 75% -M pig iron" until the chromium content of said pig iron is 19% S I I below 0.1%, thereby also lowering the manganese, silicon CaO/Si0 =1.47 and vanadiutn contents o'f'the same, thus forming a preliminarily refined iron of low' chromium content; and The pig men has the'following analysis: converting the t'hus formed pre-refinediron to steel having 3.5% f a low chromium content. 0.45% Si 2. A method of producingl-stee'l havingia. low chro- 0'.7SI%" Mn mium content from'iron ore having a high chromium 1.90% P content, comprisingthetsteps' of smelting amixtureuof 0.48% cia' first iron ore containing more than. 0.2% chromium 0.10%"V and a se'cond"ironlore'coutaining suificient manganese 0i05% S" 7 so as to form a pig iron, the proportions of said first and said second iron ores being so adjusted that the thus formed pig iron contains more than 0.2% chromium and less than 0.8% manganese; blowing said pig iron in the presence of at least one heat-consuming metal oxide until the chromium content of said pig iron is below 0.1%, thereby also lowering the manganese content of the same, thus forming a preliminarily refined iron of low chromium content; and converting the thus formed prerefined iron to steel having a low chromium content.

3. A method of producing steel having a low chromium content from iron ore having a high chromium content, comprising the steps of smelting a mixture of a first iron ore containing more than 0.2% chromium and a second iron ore containing sufficient manganese so as to form a pig iron, at least one of said iron ores also containing phosphorous, silicon and vanadium and the proportions of said first and said second iron ores being so adjusted that the thus formedpig iron contains more than 0.2% chromium and less than 0.8% manganese and also contains phosphorous, silicon and vanadium; blowing said pig iron in the presence of at least one heat-consuming oxide until the chromium content of said pig iron is below 0.1%, thereby also lowering the manganese, silicon and vanadium contents of the same, thus forming a preliminarily refined iron of low chromium content; and converting the thus formed pre-refined iron to steel having a low chromium content.

References Cited in the file of this patent UNITED STATES PATENTS Carney Oct. 27, 1908 Graef Mar. 2, 1954 OTHER REFERENCES 

1. A METHOD OF PRODUCING STEEL HAVING A LOW CHROMIUM CONTENT FROM IRON ORE HAVING A HIGH CHROMIUM CONTENT COMPRISING THE STEPS OF SMELTING A MIXTURE OF A FIRST IRON ORE CONTAINING MORE THAN 0.2% CHROMIUM AND A SECOND IRON ORE CONTAINING SUFFICIENT MANGANESE SO AS TO FORM A PIG IRON, AT LEAST ONE OF SAID IRONORES ALSO CONTAINING PHOSPHOROUS, SILICON AND VANADIUM AND THE PROPORTIONS OF SAID FIRST AND SAID SECOIND IRON ORES BEING SO ADJUSTED THAT THE THUS FORMED PIG IRON CONTAINS MORE THAN0.2% CHRCMIUM AND LESS THAN 0.8% MANGANESE, AND ALSO CONTAIN PHOSPHOROUS, SILICON AND VANADIUM; BLOWING SAID PIG IRON UNTIL THE CHROMIUM CONTENT OF SAID PIG IRON IS BELOW 0.1%, THEREBY ALSO LOWERING THE MANGANESE, SILICON AND VANADIUM CONTENTS OF THE SAME, THIS FORMING A PRELIMINARILY REFINED IRON OF LOW CHORMIUM CONTENT; AND CONVERTING THE THUS FORMED PRE-REFINED IRON TO STEEL HAVING A LOW CHROMIUM CONTENT. 